I'd like to see Node.js using Chkara by default, V8 developers have showed that they don't care much about Node.js, they are more interested in Chrome, and MS have showed more interest in Node.js than Google and I'm sure it will be better for all, fingers crossed.

This is definitely a problem today, but NAN (https://github.com/nodejs/nan) which is now the recommended way to build native modules, offers a way out. That project provides a stable API to insulate module developers from changes between v8 versions.

Sometime down the line, a NAN-spidermonkey or NAN-chakra project might become feasible.

Sort of -- in practice, we found ourselves instead playing catchup to NAN (many changes across Node 10, 12, 4, etc.). It insulates from minor changes, and increasingly, part of that has been Node waiting longer and longer between v8 changes.